ILLINOIS STATE DAIRYMEN'S ASSOCIATION. 269 



plains to the southwest and west, which lie about 5,000 feet 

 above us. At other seasons of the year, or during the fall and 

 winter months, when the area of low barometer is southeast of 

 us, over the Atlantic, the reinforcing currents will be from the 

 northwestern high plateaus. When we look for the cause of 

 this great barometric trough of low pressure, we find it due to 

 two causes : The nearness of the great lakes and the natural 

 consequence of the sun's heat upon them; and second, to the 

 added fact of immense cultivation. There is no spot on the 

 globe that presents as many consecutive square miles of 

 ploughed land as this barometric trough. During the tornado 

 period a bird's-eye view of the area would show thousands and 

 thousands of square miles of plowed land prepared for corn, or 

 only sparsely covered with oats or wheat; there is no vegeta- 

 tion to fix the sun's heat in permanent forms, and as a conse- 

 quence this heat runs riot and rampant in the atmosphere. By 

 reason of its reflection and radiation from the water soaked 

 ground and lake surface, it lifts vast columns of vapor laden, 

 heated air, that trend away to the northeast, to part with their 

 vapor and dissipate their heat, thus following the general law of 

 all super-heated streams of air and water, the world over, to 

 flow away from the equator, only to return to it by well estab- 

 lished ways as colder streams. To preserve the equilibrium or 

 to restore the lost balance caused by this uplift, a demand is 

 made on the atmosphere of adjacent regions. 



" But why is it that the country lying to the south and west 

 mainly supplies this demand? It is from the fact that during the 

 prevalence of this barometic trough the atmospheric currents 

 supplying the region come mainly from the south, being set in 

 motion over the Gulf of Mexico by just such mechanism as pre- 

 vails over the great lakes ; and these currents from the south 

 are reinforced by other currents from the great plains westward, 

 giving a resultant in the southwest winds. These causes are 

 too complicated and intricate to be dwelt on in this paper. Our 

 interest is mainly with the westward factor in the problem. To 

 fully appreciate this we must get a substantial understanding of 



